HAVANA, Feb 5 (Reuters) - Colombia's FARC rebels accused former President Alvaro Uribe on Wednesday of being involved in spying on government negotiators at peace talks in Cuba, and said their own delegation's communications had also been intercepted.

The FARC comments came a day after President Juan Manuel Santos ordered an investigation into claims of spying on his negotiators by rogue elements in Colombia's military, saying "dark forces" were trying to sabotage his bid to end five decades of war with the leftist guerrillas.

Uribe, Santos's predecessor, intensified the military's attacks on the FARC during his two terms in power from 2002-2010, using support from the United States to thin the rebels' ranks and push them into more remote jungle areas.

"Alvaro Uribe is behind all this. Do not forget that (Uribe) is the No. 1 enemy of peace in Colombia," Ivan Marquez, head of the FARC's negotiating team in Havana, told reporters.

"Not only is there spying by Colombia on the government's peace delegation, but especially on the peace delegation of the FARC," he said, without elaborating or offering evidence.

Uribe denied involvement when the spying allegations came to light on Tuesday with the publication of a 15-month investigation by weekly news magazine Semana. The former president said any suggestion that he was behind the supposed espionage was a "smoke screen."

Citing an unnamed source, the Semana report said the spying operation, code-named "Andromeda," was aimed at gathering as much information as possible about what was being discussed at the talks.

Uribe is a fierce opponent of the peace talks. He has said the FARC should be defeated militarily instead of being offered concessions and impunity or light sentences for their crimes.

According to Semana, text messages were collected, but there was no eavesdropping on telephone calls. The magazine said the spying had been carried out from a Bogota restaurant and adjoining Internet center that had been set up as a front for the operation.

Late on Tuesday, Defense Minister Juan Carlos Pinzon said two generals, including the head of army intelligence, had been relieved of duty for the duration of the investigation.

Santos set a deadline of Friday, February 14, for the investigation to be concluded. Several previous investigations announced by the government and army into information leaks relating to the peace talks in Cuba were inconclusive.

"I have given specific instructions to the Army Inspector that the investigation yield results by the end of next week at the latest," Santos said during a meeting with Justice Ministry officials.

The negotiations with the FARC began in November 2012 and have been conducted in secrecy. Both sides have abided by that except for brief communiques about their progress. (Writing by Peter Murphy; Editing by Daniel Wallis, Leslie Adler, Toni Reinhold)